1. Field of the Invention
The present embodiments relate to a radar device for a vehicle and a target measurement method therefor and, more particularly, to a radar device for a vehicle, enabling a distance and a velocity of a target approaching at a high speed in a short distance to be measured while securing a detection performance of the target, using a multi-chirp signal having different slopes, and a target measurement method therefor.
2. Description of the Prior Art
A general FMCW-type radar device for a vehicle acquires distance and velocity information using a frequency difference between a transmission signal which gradually changes over time and a reception signal which changes by a target. Here, since a demodulated signal has frequency variations generated by a distance and a velocity of the target mixed therein, a combination of an up-chirp in which frequency gradually increases over time and a down-chirp in which frequency gradually decreases over time is used in order to divide the mixed frequency variations so as to calculate the accurate distance and velocity of the target.
FIG. 1A is a diagram illustrating a transmission signal that is transmitted through a transmission antenna, and a reception signal that is the transmission signal reflected on a target and returns. FIG. 1B is a diagram illustrating a frequency difference between the transmission signal and the reception signal which are illustrated in FIG. 1A. The distance and velocity of the target are mathematically calculated based on the frequency difference between the transmission signal and the reception signal illustrated in FIG. 1B.
However, signal variation by the distance of the target is determined to be in a specific direction and frequency variation by velocity of the target changes in two directions according to the positive (+) or negative (−) velocity. Therefore, when a target that is in a close distance from a radar device and has a large velocity element is present, that is, when an object approaching at a high speed in a short distance is present, a sum of the signal velocity according to the distance and the signal velocity according to the velocity has a negative value (−), as illustrated in FIG. 2. Accordingly, there may occur a problem of an undetected or mistakenly detected target approaching at a high speed in a short distance.
There are two methods for acquiring correct target information, that is, solving a problem of an undetected or mistakenly detected target approaching at a high speed in a short distance, the methods for enabling to distinguish a negative (−) frequency value through I/Q scheme-hardware, and making the slope of a chirp signal steep so that the occurrence of such a frequency inversion phenomenon is minimized.
However, implementation of an I/Q scheme has a disadvantage of requiring additional hardware resources and calculation processing procedures, and a scheme for making the slope of a chirp signal steep has a disadvantage of deteriorating the accuracy of velocity of a high-performance ADC or a target.